Wound Healing

What is wound healing in a nutshell?

restoration of normal anatomic continuity to a disrupted area of tissue

What are the three stages of would healing?

inflammation, proliferation, and maturation

What is another term for the inflammation stage of wound healing?

debridement

What is another term for the proliferation stage of wound healing?

repair

What is another term for the maturation stage of wound healing?

remodeling

What happens during the inflammation stage of wound healing?

immediate vasoconstriction within the first 5-10 minutes followed by vasodilation as leukocytes phagocytize debris, secrete growth factors, and attract mesenchymal cells

What does vasodilation cause?

classic signs of erythema, swelling, heat

What happens during the proliferation stage of wound healing?

angiogenesis, fibroblast migration, contraction, epithelialization; granulation tissue has extensive capillary network and wound contraction via myofibroblast network, epithelial migration until contact inhibition

What is the hallmark of the proliferation stage of wound healing?

granulation tissue

What happens during the maturation stage of wound healing?

collagen changes from predominantly type III and type I reorganizing along lines of tension; can happen up to 2 years post wounding

Are the stages of wound healing mutually exclusive?

no they can overlap in the same wound

What is first intension healing?

with appropriate apposition of tissue layers (subcutaneous tissue, skin), healing may occur via reepithelialization at a rate of 1mm/day

What are the two types of first intention healing?

primary closure and delayed closure

What is primary closure?

healing of a sutured surgical incision

What is delayed closure?

closure after 2-5 days, PRIOR to formation of granulation tissue

What is second intention healing?

healing of a wound without suturing; usually involves wound contraction and epithelialization

What is third intention healing?

suturing of a wound AFTER the formation of granulation tissue

What percentage of normal strength does wounded skin have at 14 days postop?

5-10%

What percentage of normal strength does wounded skin have at 3-4 weeks postop?

~25%

What is the ultimate strength of wounded skin several months postop?

70-80%

What are the characteristics of healing tissue in the gastrointestinal tract?

collagen breakdown secondary to collagenous activity within the wound occurs in the first 1 to 2 days of the healing process

What layer of the GI tract provides the most tensile strength?

submucosa because its 68% type I collagen

What are the characteristics of healing tissue of fascia?

due to being relatively avascular and acellular it may have a prolonged inflammatory response taking up to 6 months to regain 80% strength

What are the characteristics of healing tissue in the urinary bladder?

regains 100% of its strength within 21 days since mucosal injury can reepithelialize within 2-4 days; normally very low basal mitotic activity so growth factors upregulated in response to injury

What are the characteristics of healing tissue of bone??

fractures heal by combination of intramembranous and endochondral ossification but endomembranous ossification predominate; regains 100% of strength but maturation phase can take over a year

What are the gender difference in healing?

superior healing in intact females compared to intact males; androgens (male) appear to have a negative impact on wound healing and increased susceptibility to wound infection

How does human and porcine skin primarily heal?

epithelialization

How does rodent and other loose-skinned mammal skin primarily heal?

contraction

How does the loose skin over trunk and neck in dogs primarily heal?

contraction

How does the tighter skin on extremities in dogs primarily heal?

epithelialization

What are female hairless dogs and female Red Duroc pigs prone to?

fibroproliferative scarring, similar to keloids in human beings

How do cat wounds heal?

contraction at wound edge primarily

How do dog wounds heal?

central “pull” of fibroblasts and epithelialization

What are the local factors affecting healing?

tension, motion, fluid accumulation, infection, decreased skin perfusion, and self-mutilation

How does tension affect healing?

any tension on wound edges could disrupt cutaneous perfusion and retard wound healing

How does motion affect healing?

repeated shearing forces negatively impact wound healing

How does fluid accumulation affect healing?

ideal medium for bacteria, difficult for inflammatory cells to adequately function, difficult for antibiotics to penetrate

How does infection affect healing?

contamination → infection → ± septicemia

How does decreased skin perfusion affect healing?

hypovolemia, hypothermia, fluid accumulation, excision of subcutaneous tissue, excessive pressure from bandages can cause

How does self-mutilaiton affect healing?

can cause mild inflammation to complete disruption of the wound bed and infection

What are the systemic factors that affect healing?

immunosuppression, neoplasia, geriatric age, malnutrition, uremia

How does immunosuppression affect healing?

secondary to primary diseases (FIV, Cushing’s disease), or to administration of glucocorticoid (disrupts collagen synthesis) or chemotherapeutics

How does neoplasia affect healing?

treatment often involved chemotherapy and/or radiation therapy, cancer-associated malnutrition

How does geriatric age affect healing?

decrease cutaneous perfusion, increase skin fragility, increased risk for infection

How does malnutrition affect healing?

delayed neovascularization, decreased collagen synthesis, prolongation of inflammation, decreased leukocyte phagocytosis, B and T cell dysfunction, and decreased mechanical skin strength

How does uremia affect healing?

associated with slower epithelialization